The reaction mechanism of the Na-K pump of the red blood cell will be investigated. The effects of ions at the inner and outer surface of the pump and the metabolites at the inner surface of the pump on the pump rate will be determined and from the results of such studies conclusions about the pump rate will be drawn . The studies will focus on three main areas. Internal K produces a significant stimulation of the pump rate; we shall attempt to determine which step in the reaction sequence of the pump is increased by internal K, and whether internal K alters the reaction of the pump with ATP, ADP or inorganic phosphate. Second, we will attempt to determine the characteristics of the interaction of Mg with the pump and we will perform experiments to determine the site at which Mg competes with the inhibitor oligomycin. Finally, we will attempt to determine from steady state kinetic measurements the number of sites at which inorganic phosphate and arsenate interact with the pump and whether pump inhibition by these ions is competitive with ATP.